The incorporation of a self venting device in liquid dispensing spouts has long been recognized as a desirable aid in providing smooth, surge free pouring. One type of pouring spout commonly used on industrial size pails and cans consists of a collapsible spout having a flexible wall portion which allows the spout to be raised from a compact stored or nested condition to a fully extended pouring position. These prior art pouring spouts are available incorporating a self vent device which eliminates the need for a completely separate and more costly vent in the head of the container. In general terms such vent devices consist of an elongated tubular member having a circumferentially outwardly disposed flange at its lower end. With the spout in nested or stored position the upper portion of the tubular vent is affixed to the spout interior with the major portion of the vent extending axially beyond the spout into the container. Upon raising the flexible spout to extended pouring position the vent member is also axially displaced bringing the vent flange closely adjacent the spout base and providing a series of air entry passages therebetween.
The above described prior art constructions while adequately performing their intended venting functions possess certain structural deficiencies which this invention overcomes. Of principal concern, the rather considerable overall axial elongation of the collapsed or nested closure as results from incorporation of the prior art tubular vent constructions has serious drawbacks. For example, it is common practice for the pail manufacturer to furnish heads complete with closure independently of pail bodies which bodies are stacked nested within each other to reduce shipping costs. It is also the practice to stack pail covers, however, that is virtually impossible with a pouring vent which doubles the vertical profile of the closure. In fact, even shipment of the closures per se becomes more costly as a result of the substantially increased bulk due to the prior art self vent. A further drawback resides in the necessity of securely affixing the vent member within the spout interior during manufacture. This fabrication is normally performed as a heat sealing operation which is not only costly but must be consistently strong enough to prevent separation during shipment and handling. Also, once the vented closure is applied to a filled pail the tendency of the vent to separate from the spout becomes even greater due to the mechanical sloshing action of the fluid. Chemical attack alone by the packaged fluid may severely stress the heat sealed joint between the spout and vent.